Define the internal driver API for vol wiping

Also add vol wiping to ESX storage driver struct

src/driver.h

@@ -722,6 +722,10 @@ typedef int
     (*virDrvStorageVolDelete)               (virStorageVolPtr vol,
                                              unsigned int flags);
 
+typedef int
+    (*virDrvStorageVolWipe)                  (virStorageVolPtr vol,
+                                              unsigned int flags);
+
 typedef int
     (*virDrvStorageVolGetInfo)               (virStorageVolPtr vol,
                                               virStorageVolInfoPtr info);
@@ -791,6 +795,7 @@ struct _virStorageDriver {
     virDrvStorageVolCreateXML volCreateXML;
     virDrvStorageVolCreateXMLFrom volCreateXMLFrom;
     virDrvStorageVolDelete volDelete;
+    virDrvStorageVolWipe volWipe;
     virDrvStorageVolGetInfo volGetInfo;
     virDrvStorageVolGetXMLDesc volGetXMLDesc;
     virDrvStorageVolGetPath volGetPath;

src/esx/esx_storage_driver.c

@@ -102,6 +102,7 @@ static virStorageDriver esxStorageDriver = {
     NULL,                                  /* volCreateXML */
     NULL,                                  /* volCreateXMLFrom */
     NULL,                                  /* volDelete */
+    NULL,                                  /* volWipe */
     NULL,                                  /* volGetInfo */
     NULL,                                  /* volGetXMLDesc */
     NULL,                                  /* volGetPath */